Diode strings are for example used for ESD (Electrostatic Discharge) protection of integrated circuits. In particular, via such a diode string an ESD pulse may be shunted to a supply voltage like VDD or VSS. In some cases, diodes of such diode strings are formed using well structures. However, in some circumstances like overvoltage at a pad to be protected, i.e. a voltage outside a normal range, but below typical ESD voltages, and/or turned off supply voltages, parasitic bipolar transistors formed by the above mentioned well structures may become conducting leading to undesired leakage currents.